1. Field of the Invention
The present invention relates to spindle motors for disk drives. More particularly, the present invention relates to a disk drive comprising a spindle speed fault detector for retracting a head independent of a servo microprocessor when a spindle speed fault mode is detected.
2. Description of the Prior Art
Magnetic disk drives employ a head which is actuated over the surface of a spinning disk for writing and reading data to and from concentric data tracks. As the disk spins, a thin layer air-bearing forms between the head and the disk such that the head is said to xe2x80x9cflyxe2x80x9d just above the surface of the disk. A voice coil motor (VCM) actuates the head over the disk and a spindle motor, typically implemented as a brushless DC motor, controls the rotation of the disk about a spindle. A power driver chip comprises a VCM driver which drives the VCM motor and a spindle driver which drives the spindle motor. A servo microprocessor executes the steps of a servo control program to control the VCM and spindle drivers, thereby controlling the position of the head and angular velocity of the disk.
When the disk spins down such that the thin layer air-bearing dissipates, it is important to retract the head to prevent it from contacting into the surface of the disk and corrupting the recorded data. The disk may spin down for various reasons, for example, when put into an idle mode, when power is shut off or fails, or when the servo microprocessor malfunctions and is no longer servicing the spindle motor driver. If the power is shut off expectedly or the disk drive is put into an idle mode, the servo microprocessor will execute a controlled head park procedure wherein the head is retracted from the data area of the disk and parked in a safe location (e.g., in a landing zone on the disk or on a ramp). A disk controller may also monitor the speed of the spindle motor and issue a command to the servo microprocessor to park the head in the safe location if the spindle speed drops below a predetermined threshold. This might occur, for example, if there is a problem with the mechanics of the spindle motor or with the circuitry in the spindle motor driver.
In exigent situations where the head must be parked independent of the servo microprocessor (e.g., when the power fails or is shut off unexpectedly, or when a watchdog timer detects that the servo microprocessor has malfunctioned), a park circuit within the VCM driver has been employed to automatically park the head. For example, a special power failure circuit has been employed to monitor the power in a disk drive and park the head using the park circuit if the power fails. Similarly, a watchdog timer has been employed to detect when the servo microprocessor has malfunctioned (e.g., when it has entered an infinite loop). The watchdog timer must be serviced periodically by the servo microprocessor, otherwise the head is automatically parked and the servo microprocessor is reset.
Although the aforementioned prior art techniques are adept at detecting certain anomalous situations, such as power failure or certain servo microprocessor failures, there are other situations which can still cause the head to contact the disk. For example, the microprocessor can malfunction with respect to the spindle motor driver and/or a park command issued by a disk controller, but not malfunction with respect to the watchdog timer. When this happens, the watchdog timer will not park the head even though the spindle motor may be losing speed due to the servo microprocessor not servicing the spindle motor driver. Other possible scenarios include the watchdog timer failing, or the watchdog timer being disabled during development so that the servo microprocessor is not automatically reset when a malfunction occurs. The watchdog timer may be disabled during development in order to preserve the state information of the servo microprocessor which can provide valuable insight into the cause of a servo microprocessor malfunction. Yet another situation unaccounted for by the prior art is when a single clock (e.g., a crystal) is used to drive both the servo microprocessor and the watchdog timer. If this clock fails and the spindle motor loses speed, neither the servo microprocessor nor the watchdog timer can issue a command to park the head.
There is, therefore, the need to improve upon the prior art techniques for parking the head independent from the servo microprocessor in exigent situations, including when the servo microprocessor malfunctions in a manner undetectable by a watchdog timer, when the watchdog timer has been disabled or malfunctions, or when the servo microprocessor clock fails.
The present invention may be regarded as a disk drive comprising a disk having a data area, a head, a spindle motor for spinning the disk, and an actuator for positioning the head over the data area during a spindle speed control mode, and retracting the head away from the data area during a spindle speed fault mode. A servo microprocessor executes steps of a servo control program to generate a first control signal. An actuator driver circuit is responsive to the first control signal for controlling the actuator during the spindle speed control mode. A spindle speed detector generates a spindle speed signal representing a spin rate of the spindle motor, and a spindle speed fault detector is responsive to the spindle speed signal for detecting the spindle speed fault mode and generating a second control signal in response to the detected spindle speed fault mode. The actuator driver circuit is responsive to the second control signal so that the actuator retracts the head away from the data area independent of the servo microprocessor during the spindle speed fault mode.
The present invention may also be regarded as a method of detecting a spindle speed fault mode in a disk drive and, in response to detecting the spindle speed fault mode, retracting a head away from a data area of a disk independent of a servo microprocessor for controlling a spindle motor within the disk drive, the spindle motor for spinning the disk. The method comprises the steps of generating a spindle speed signal representing a spin rate of the spindle motor, processing the spindle speed signal to detect a spindle speed fault mode, and in response to detecting the spindle speed fault mode, retracting the head away from the data area independent of the servo microprocessor.